Functionalized silicas

ABSTRACT

Functionalized silicas with 3-methacryloxypropylsilyl and/or glycidyloxypropylsilyl groups on the surface are prepared by mixing the silicas with the silane and heat-treating the mixture. The silicas are employed, for example, in solvent-containing coatings.

INTRODUCTION AND BACKGROUND

[0001] The present invention relates to functionalized silicas, a process for their preparation and their use. It is known to react silicon dioxide obtained by flame hydrolysis and with a surface area of 40 to 200 m²/g with 3-methacryloxypropyltrimethoxysilane. The resulting silicon dioxide is then coated with a further shell of (meth)acrylate polymers and subsequently employed in dental compositions (EP 0 142 784 A1).

SUMMARY OF THE INVENTION

[0002] The present invention provides functionalized silicas, characterized by functional groups fixed on the surface, the groups being 3-methacryloxypropylsilyl and/or glycidyloxypropylsilyl.

[0003] The present invention also provides a process for the preparation of the functionalized silicas, which is characterized in that a silica is sprayed optionally first with water or dilute acid and then with a surface modification reagent or a mixture of several surface modification reagents in a suitable mixing vessel, with intensive mixing, the components are optionally re-mixed for 15 to 30 minutes and heat-treated at a temperature of 100 to 400° C. over a period of 1 to 6 h.

[0004] A silica prepared pyrogenically by the route of flame hydrolysis of SiCl₄ can preferably be employed as the silica. Such pyrogenic silicas are known from Ullmanns Enzyklopädie der technischen Chemie [Ullmanns Encyclopaedia of Industrial Chemistry], 4th edition, volume 21, page 464 (1982).

[0005] In a preferred embodiment of the invention, a pyrogenic silica with a surface area of approx. 200 m²/g can be employed (Aerosil® 200).

[0006] Monomeric substances, such as 3-methacryloxypropyltrialkoxysilane and/or glycidyloxypropyltrialkoxysilane, wherein alkoxy can be methoxy, ethoxy and/or propoxy, can be employed as the surface modification reagent.

[0007] The amount of silane can be metered with respect to the silica such that no or only a small excess results. The excess silane can optionally be removed during the heat treatment.

[0008] The silica according to the invention can be employed in solvent-containing coatings, for example 2-component polyurethane coatings.

DETAILED DESCRIPTION OF INVENTION

[0009] The functionalized silicas according to the invention have the following advantages: When used in solvent-containing coatings, such as, 2-component polyurethane coatings, the scratch resistance of the coating surface is increased.

[0010] According to the invention, the pyrogenically prepared silicas according to table 1 can be employed as the silica for the silanization. TABLE 1 Physico-chemical data of AEROSIL ® AEROSIL AEROSIL AEROSIL AEROSIL AEROSIL AEROSIL AEROSIL AEROSIL Test method 90 130 150 200 300 380 OX50 TT600 Behaviour towards hydrophilic water Appearance loose white powder BET surface area¹⁾ m2/g 90 ± 15 130 ± 25 150 ± 15 200 ± 25 300 ± 30 380 ± 30 50 ± 15 200 ± 50 Average primary nm 20 16 14 12 7 7 40 40 particle size Tamped density g/l 80 50 50 50 50 50 130 60 approx. values²⁾ Compacted goods g/l 120 120 120 120 120 120 (added “V”) VV goods g/l 50/75 50/75 50/75 (added “VV”)¹²⁾ g/l 120 120 Loss on drying³⁾ % <1.0 <1.5 <0.5⁹⁾ <1.5 <1.5 <2.0 <1.5 <2.5 (2 hours at 105° C.) on leaving supply works Loss on ignition⁴⁾⁷⁾ % <1 <1 <1 <1 <2 <2.5 <1 <2.5 (2 hours at 1000° C.) pH⁵⁾ 3.7-4.7 3.7-4.7 3.7-4.7 3.7-4.7 3.7-4.7 3.7-4.7 3.8-4.8 3.6-4.5 SiO₂ ⁸⁾ % >99.8 >99.8 >99.8 >99.8 >99.8 >99.8 >99.8 >99.8 Al₂O₂ ⁸⁾ % <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.08 <0.05 Fe₂O₃ ⁸⁾ % <0.003 <0.003 <0.003 <0.003 <0.003 <0.003 <0.01 <0.003 TiO₂ ⁸⁾ % <0.03 <0.03 <0.03 <0.03 <0.03 <0.03 <0.03 <0.03 HCl⁸⁾¹⁰⁾ % <0.025 <0.025 <0.025 <0.025 <0.025 <0.025 <0.025 <0.025 Sieve residue⁸⁾ % <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.2 <0.05 (Mocker method, 45 μm) Drum size (net)¹¹⁾ kg 10 10 10 10 10 10 10 10

EXAMPLE 1

[0011] Aerosil® 200 is mixed with 4 parts water and 18 parts 3-methacryloxypropyltrimethoxysilane (for example DYNASILAN MEMO) and the mixture is heat-treated at 140° C. under an inert gas.

[0012] The silica obtained has the following properties: BET [m²/g] 138 Tamped density [g/l] 52 pH 4.6 C content 5.7 Loss on drying [%] 0.8 Loss on ignition [%] 9.7 DBP number [%] 228

EXAMPLE 2

[0013] Aerosil® 200 is mixed with 3 parts water and 16 parts 3-glycidyloxypropyltrimethoxysilane (for example DYNASILAN GLYMO) and the mixture is heat-treated at 140° C. under an inert gas.

[0014] The silica obtained has the following properties: BET [m²/g] 165 Tamped density [g/l] 53 pH 4.9 C content 5.5 Loss on drying [%] 1.5 Loss on ignition [%] 8.7 DBP number [%] 242

[0015] Experiment 1

[0016] A conventional 2-component polyurethane coating has been used to investigate the improvement in the scratch resistance. The recipe for the coating and the preparation, including the application, are summarized in the following: Parts by Recipe: wt. Millbase Setalux C 1152, 53.3 XX - 51.50% (Akzo Nobel) Butyl acetate 98%  6.7 Xylene  6.7 AEROSIL (silica according to example 1)  5.0 Σ 71.7 Lacquer Setalux C 1152,  1.1 constituents: XX - 51.50% (Akzo Nobel) Xylene 12.2 Ethoxypropyl acetate  1.5 Butylglycol acetate  1.5 Hardener: Desmodur N 75 (Bayer) 17.0 Σ 105.0 

[0017] Preparation and Application of the Coatings

[0018] The Setalux is mixed with the solvents. For predispersion, the AEROSIL® is then incorporated into this mixture with a dissolver (disc Ø 45 mm) and predispersed for 5 min at 2000 rpm. The mixture is dispersed in a laboratory bead mill for 30 min at 2500 rpm and a pump output of 60% using glass beads (Ø approx. 1 mm). The dispersing quality is checked with a grindometer, 25 μm, in accordance with DIN ISO 1524. It must be smaller than 10 μm.

[0019] The lacquer constituents are added to the millbase in accordance with the recipe, the components being mixed with a blade stirrer at 2000 rpm. The hardener is stirred into the mixture in the same manner.

[0020] After the coatings have been adjusted to the spray viscosity according to DIN 53411, the coatings are applied to black-lacquered metal sheets, for example DT 36 (Q-Panel), by means of spraying application (layer thickness about 40-50 μm). After the spraying, the metal sheets are dried for 24 h at room temperature and then for 2 h in a drying oven at 70° C.

[0021] Scratching Experiments:

[0022] The metal sheets are scoured with a quartz/water slurry (100 g water+1 g Marlon A 350, 0.25%+5 g Millicarb BG) with the aid of a scouring and washing resistance testing machine (Erichsen, brush with pig bristles). The shine before and 10 min after scouring is determined with a reflectometer (20° incident angle). TABLE 2 Summary of the coating-relevant properties of the liquid coatings and of the films applied and dried: AEROSIL Silica/(example 200 1) Reference Grindometer value [μm] <10 <10 — Viscosity (millbase) [mPas]  6 rpm 1000 180 60 rpm 464 600 143 Viscosity [mPas] (coating + hardener)  6 rpm 166 180 75 60 rpm 141 147 62 Dilution (adjustment [%] 11.5 8.5 1.7 to 20 s DIN 4 mm) Scratch resistance 20° reflectometer value before 90.9 87.6 91.3 scratching 40 strokes with Sikron F 500 66.4 73.0 50.7 20° reflectometer value residual 73.0 83.3 55.5 shine 100 strokes with Millicarb 79.2 80.5 68.4 BG 20° reflectometer value residual 87.1 91.9 74.9 shine [%]

[0023] Further variations and modifications of the foregoing will be apparent to those skilled in the art and are intended to be encompassed by the claims appended hereto.

[0024] European priority application 00 122 954.1 is relied on and incorporated herein by reference. 

We claim:
 1. A functionalized silica, having at least one functional group fixed on the surface of said silica, the group being selected from the group consisting of 3-methacryloxypropylsilyl, glycidyloxypropylsilyl and mixtures thereof.
 2. The functionalized silica according to claim 1 wherein the silica is produced by flame hydrolysis.
 3. A process for the preparation of the functionalized silica according to claim 1, comprising spraying a silica optionally first with water or dilute acid and then with a surface modification reagent or a mixture of surface modification reagents in a mixing vessel, with intensive mixing, optionally re-mixing said silica for 15 to 30 minutes and heating at a temperature of 100 to 400° C. over a period of 1 to 6 h.
 4. The process according to claim 3 wherein the surface modification agent is a member selected from the group consisting of 3-methacryltrialkoxysilane, glycidylotrialkoxysilane and mixtures thereof.
 5. A surface coating with a coating containing the functionalized silica according to claim
 1. 6. A coating composition comprising the functionalized silica of claim 1 and a solvent.
 7. A coating composition for preparing a scratch resistant coating on a surface, comprising the functionalized silica according to claim 1 and a polyurethane. 